Introduction
In communicating, it is certain that you cannot escape from the name communicate. Nowadays, communication technology has developed rapidly, especially wireless technology. This wireless communication technology can reach areas that cannot be reached by wireline communication technology. This technology is called a microwave communication network, with a transmission system using microwaves and antennas as a tool to transmit signals so that they can communicate with each other.
In the use of wireless transmission, it is inseparable from obstacles that cause disruption in the information delivery process. One of the causes of disruption of microwave transmission is fading. Fading is a phenomenon of signal fluctuations that cause decreased reception and damage to transmission quality (Anggi, 2020). Therefore, a reliability value is needed in a network system in order to obtain optimal system conditions. The measure of the reliability of a system is called availability. Therefore, optimization is needed to increase the availability of the microwave communication system by using diversity techniques that can increase the reliability value of the system in the communication network.
Diversity is a technique of operating two or more systems or subsystems simultaneously (redundancy) to increase system reliability (availability) by reducing fading due to propagation phenomena such as reflection, diffraction, refraction, scattering, or attenuation. The purpose of this diversity is to ensure equipment availability and ensure path availability. There are various types of diversity as follows:
In communicating, it is certain that you cannot escape from the name communicate . Nowadays, communication technology has developed rapidly, especially wireless technology. This wireless communication technology can reach areas that cannot be reached by wireline communication technology. This technology is called a microwave communication network, with a transmission system using microwaves and antennas as a tool to transmit signals so that they can communicate with each other.
In the use of wireless transmission, it is inseparable from obstacles that cause disruption in the information delivery process. One of the causes of disruption of microwave transmission is fading. Fading is a phenomenon of signal fluctuations that cause decreased reception and damage to transmission quality (Anggi, 2020). Therefore, a reliability value is needed in a network system in order to obtain optimal system conditions. The measure of the reliability of a system is called availability. Therefore, optimization is needed to increase the availability of the microwave communication system by using diversity techniques that can increase the reliability value of the system in the communication network.
Diversity is a technique of operating two or more systems or subsystems simultaneously (redundancy) to increase system reliability (availability) by reducing fading due to propagation phenomena such as reflection, diffraction, refraction, scattering, or attenuation. The purpose of this diversity is to ensure equipment availability and ensure path availability. There are various types of diversity as follows:
1. Frequency Diversity
Frequency diversity is a system that operates two microwave frequencies on one antenna, both at the transmitter and receiver. The difference in carrier frequencies used to transmit information is used with a range of 2-5%
The way frequency diversity works
is:
If the transmission system uses frequency diversity techniques to overcome fading, the following improvement factors will be obtained:
\[ l_{fd} = \frac{0.8 \cdot \Delta f}{f^2 \cdot D} \cdot 10^{\frac{F}{10}} \] \[ \begin{aligned} \text{where:} \quad & \Delta f = \text{frequency separation (GHz)} \\ & F = \text{fade depth (dB)} \\ & f = \text{carrier frequency (GHz)}, \quad 2 \leq f \\ & D = \text{hop length (km)}, \quad 30 \leq D \end{aligned} \]Applications of frequency diversity such as
a. Spread spectrum
FHSS (Frequency Hoping Spread Spectrum)
FHSS changes frequency search engine in a way dynamic (hopping) based pseudorandom sequence known to both the transmitter and receiver. If one frequency experience disturbance , system will direct switch to other higher frequencies good . Example application such as Bluetooth, wireless sensors .
b. OFDM (Orthogonal Frequency Division Multiplexing)
In OFDM, the stream speed tall divided become many high-speed subcarriers low transmitted in parallel. On each subcarrier has a narrow bandwidth , is orthogonal or No each other bother although frequency adjacent . Frequency diversity can applied to OFDM because
Distribution signals on multiple subcarriers
OFDM divides high speed data stream tall become many subcarriers at speeds low transmitted in parallel . Each subcarrier has a narrow bandwidth and is orthogonal so that No each other disturbed although the spectrum overlap overlap.example its application is on 4G/5G network and also Wi-Fi 802.11ax
Adaptation against selective fading
GI (Guard Interval) on the addition of Cyclic Prefix (CP) will eliminate intersymbol interference due to from multipath. GI allows reception multipath signal as diversity gain and not interference . Then the frequency equalizer , here will to compensate rotation phase and attenuation per subcarrier using pilot symbols. Its application is on 5G Massive MIMO and underwater Communication.
2. Space Diversity (Antenna Diversity)
Space diversity is a method of signal transmission with transmit replica the signal that same through different antennas. space diversity offers different paths without increasing transmitter power or bandwidth. The consequence of installing this technique is that 2 or more receiving antennas and 2 or more RF stages are required at the receiver. The antennas used to transmit the signal must be spaced so that the channel gain is independent of the signal path. The distance used ranges from 100-200m. There are several space diversity methods , including
a. Selection diversity
Instant SNR branch highest connected to the demodulator, the signal antenna That Alone can taken the sample and the signal best sent to One demodulation
b. Feedback diversity
N- signal scanned on the side recipient until One signal found be on top threshold that has been determined . Signal accepted until signal be under threshold , scanning process started Again .
c. Maximal ratio combining technique
Signal from all branch N is given weight in accordance with SNR and then summed up . Signal must dicophase . Output SNR = Sum from each SNR.
d. Equal gain combining technique.
Weight branch everything set up become one . Signal from every antenna dicophase . Utilizing energy in all branch . Its performance A little more low than MRC and more superior than diversity selection .
The way to calculate spatial diversity is as follows: \[ I = S \cdot \frac{1.2 \times 10^{-3} \cdot f^2 \cdot 10^{(F - V)/10}}{d} \] \[ \begin{aligned} \text{where:} \quad & S = \text{vertical spacing of the antennas (m), center to center (5--15 m)} \\ & f = \text{frequency (Hz)} \\ & V = \text{difference in gain between two antennas} \\ & d = \text{hop length (km)} \\ & F = \text{fade depth (dB)} \end{aligned} \]
3. Time Diversity
Time diversity is a method of signal transmission by retransmitting the same signal at separate time intervals. The retransmitted signal must be smaller than the coherence time. Time diversity does not require amplification of the transmission power. Time diversity can realized with various ways such as
a. Repetition coding
There are 3 mechanisms Work from repetition coding
1. Transmission repetitive
In this process data is sent in multiple time slots separately ( example t1, t2, t3). If fading occurs at t1, the signal at t2 or t3 is still intact .
2. Interleaving
Data is interleaved for spreading errors due to temporary fading , for example in The FSO (free-space optical) interleaving system utilizes time diversity order (TMO) to mitigation turbulence atmosphere .
3. Combination on receiver
Receiver combines all Signal Copies using MRC for give weight more large on high SNR signals and SC for select Copy with quality best .
b. Automatic Repeat Request (ARQ)
Automatic repeat request is method control Where the receiver will be send an acknowledgement (ACK) if package accepted with correct . Otherwise , the transmitter will repeat delivery package , this used in the network such as Wi-Fi, TCP. Time diversity plays a role in retransmission at different times and sliding window protocols. The advantages of ARQ with time diversity are improvement reliability Where combination signal from time different reduce probability decoding failure, spectral efficiency is reduce need redundancy code versus forward error correction (EFC), and adaptability that is No need information condition channel (CSIT) at the sender . The application of ARQ is in the TCP protocol which adopts selective repeat ARQ variation with SACK for internet data transmission .
Combination of interleaving and coding
Interleaving is a composition technique rewrite bits or data before transmitted with objective spread burst errors into more random errors easy For corrected . Coding or channel coding is the process of adding redundant bits to detect and correct errors. How it works there is encoding Where the data will be encoded with code error correction and also in this process redundant bits will be added For error protection , then there is an interleaving process where the bits will arranged in matrix and read in a way random or No sequentially . Next transmission through the channel, here interleaving ensures that the symbols affected by fading do not sequentially due to selective fading time influence some symbols. And the last process namely decoding, in this process deinterleaving occurs or return original bit sequence .
Angle Diversity
Angle diversity is a transmission method that allows the same antenna to be placed in the same position but have different patterns. These 2 same antennas with different patterns will provide different paths for various signal paths or multipath signals. Because of the multipath , the signal own different lengths and travel times and cause variations in signal strength.
This angle diversity method No always succeed its use , if one of track problematic , path others may not affect much. Thus allowing the receiver to select the strongest signal or combine several signals to strengthen the overall signal strength. There are several methods for signal enhancement in the angle diversity method by combining the received signals. from corner different like
Diversity Selection : This method only select the strongest signal among the signals received at the moment certain.
Equal Gain Combining (EGC): EGC combines all received signals with equal weight, averaging the signal strength and minimizing effect fading.
Maximal Ratio Combining (MRC): MRC optimizes the combination of signals by weighting each signal based on its strength and phase. This technique provides the maximum signal-to-noise ratio (SNR) and offers the best performance in terms of minimize fading effect .
Advantages of Angle Diversity:
Enhanced Signal Strength: By combining signals from different paths, angle diversity effectively overcomes fading and improves overall signal strength.
Enhanced Reliability: Using multiple paths reduces the chance of losing the signal completely, making communications more reliable, especially in challenging environments.
Capacity Building: Diversity of angles can increase capacity system communication with allow transmission more lots of data through the available bandwidth .
The implementation of this angle diversity is in the form of
Multi antenna configuration
The advantages of angle diversity in multi-antennas include: that is multipath fading reduction Where the signal from direction different experiencing independent fading , increasing MIMO capacity Where the angle come different enables spatial multiplexing, and Efficiency Where overlapping coverage increases link reliability . Here is types antenna that applies angle diversity
Directional Antenna with Orientation Different
Sectorization : every antenna directed to different angles (30, 60 , 90) and used in LTE/5G base stations for overlapping coverage.
Adaptive Antenna with Beam Steering
This antenna change beam direction dynamic . Benefits from antenna This that is reduce interference and increase the gain. Example its implementation there is passive MIMO 5G which uses beamforming to track movement user
Multi-lobe Antenna
Multi-lobe Antenna own some lobe radiation main , useful For catch signal from direction different in a way simultaneous and used in radar and communication systems satellite .
Combination of Techniques
Selection combining (SC)
The mechanism of selection combining that is with choose One antenna with the highest SNR from a number of oriented antenna different . This technique suitable For system with complexity low . Benefits from use of this SC is its simple and effective implementation For environment with sporadic fading . Example its application such as Cellular Base Station and Wi-Fi.
Equal Gain Combination (EGC)
The EGC mechanism is with merge signal from all antenna with the same gain but to compensate phase For coherence . The advantages of EGC are: No need channel amplitude estimation and more Good than SC because utilise all antenna . Example its application is on radar and 5G Massive MIMO.
Maximal Ratio Combination (MRC)
The mechanism of MRC is give weight signal based on SNR each antenna before combined . Benefits from MRC which is optimal for diversity Because maximize output SNR and also reduce selective fading effect . Example MRC application is 5G MIMO system and communications satellite .
The application of angle diversity is as following
Network mobile : Help guard reliable communication in urban areas with propagation environments complex signals .
Wireless LAN : Increase data speed and coverage in indoor environments room with obstacle .
communications : Angle diversity help overcome fading atmosphere and enhance quality data transmission .
Polarization diversity
Polarization diversity is method transmission that utilizes polarization radio waves (horizontal and vertical) for creating two independent channels due to fading in polarization different tend No correlated , This technique increase reliability signal .
Implementation of polarization diversity
Cross polarized antenna
Polarization diversity can applied to cross polarized antenna Because Polarization different experiencing fading that is not correlated . If the signal polarization vertical obstructed , horizontal signal may be Still strong . Then Because efficiency space and cost , compared with spatial diversity (2 antennas separate ) cross polarized more compact ( one unit replaces 2 antennas ), no need distance large physique ( because polarization Already different )
MIMO (Multiple Input Multiple Output)
Polarization diversity is one approach For increase capacity , reliability , and spectral efficiency in MIMO. MIMO systems utilize multiple antennas at the transmitter and receiver to send a number of parallel data flow and increase resilience signal to interference . Polarization diversity works in MIMO with decorrelation signal ( Different Polarization reduce correlation inter-channel (low ECC < 0.05)), efficiency space (No need for distance physique big inter-antenna ), and compatibility with antenna array ( allows integration in compact cross-polarized antenna ). The implementation of polarization in MIMO such as design cross polarized antennas (Dual-Polarized Antennas (+-45) and Circular Polarized Antennas.), 5G massive MIMO, Wi-Fi 6, satellite , and IoT.
References
https://www.geeksforgeeks.org/diversity-and-its-types/
https://en.wikipedia.org/wiki/Diversity_combining
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PERANCANGAN LINK TRNASMISI MIKROWAVE MENGGUNAKAN TEKNIK SPACE DIVERSITY (Yus Natali)
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